1. Field of the Invention
The invention relates to the multiplexing of data from a plurality of paths into a single serial bit stream and to the demultiplexing of data from a serial bit stream into a plurality of separate paths. The invention further relates to high speed (.gtoreq.1/2 gHz bit rate) data transmission between separated complex data processors and more particularly to efficient data transmission between discrete integrated circuits using optical transmission paths.
2. Description of the Prior Art
The means for transmission of data streams between discrete information processors now frequently sets limits on the degree of complexity that may be achieved in a single monolithic device. An integrated circuit which operates at 32 bit accuracy may require 32 terminals for parallel input connection and a like 32 terminals for parallel output connection. Terminals which can only be sited at 0.010 inch centers, thus quickly consume a large part of the available perimeter of an integrated circuit. If the data processing is more complex, as for instance, the conjugation of a 64-point complex matrix, parallel input connections alone would require 4096 sites. Such a pin count would be impractical for even the current large (0.500.times.0.500 inches) chips.
The solution to the data transmission issue posed above is to increase the serialization of the data and to increase the data transmission rate per channel. The solution for megahertz transmission rates has been to use ever higher frequency electrical transmission lines. Flying leads, which are popular and low "tech", lose efficiency at quite modest frequencies, and as suggested earlier, customarily consume 0.10 inches of chip perimeter per connection.
The demand for greatly increased data rates has led to optical communication paths. An optical fiber carrying coherent light can theoretically carry data at a rate commensurate with the optical frequency. Thus the optical fiber offers the possibility of increasing the data transmission rates by more than five orders of magnitude over an electrical transmission line. In practical optical transmission paths, modulated optical carriers have achieved data modulation bandwidths at fractional (i.e. 1/2) gHz bit rates and above. Thus it is practical to transmit 32 channels each of 15 mHz bandwidth, on a single optical fiber. In this example a 32 to 1 reduction in connection pins may be achieved by multiplexing the 32 channels into a single serial data stream and then converting the electrical signal to an optical format for transmission by an optical fiber.
The use of optical fibers for high bit-rate data transmission is well known. The present invention addresses the problem of high bit-rate data transmission in the context of the requirements of monolithically integrated circuit structures. In this context, it addresses the problem of multiplexing a large number of separate sources of data in an electrical format into a serial optical data stream, and the reverse process of demultiplexing a serial optical data stream into a large number of electrical paths.